Conventionally, as a technique intended “to obtain a DC power unit that reduces harmonic components of an input current to optimally improve power factor”, the technique is proposed such that “when an AC voltage of an AC source passes at a zero point, switching means is made to perform a closing operation after a preset first delay time from the pass time and switching means is made to perform an opening operation after a preset second delay time from the pass time. (Patent Literature 1)
Further, as a technique intended “to lower a processing speed in control, to improve power factor, to reduce harmonics, and to achieve low cost by reducing the frequency of switching to achieve a minimal switching frequency”, the technique is proposed such that “there are provided a rectification circuit 2 that rectifies the voltage of an AC source 1, a smoothing capacitor 4 that smoothes the output voltage from the rectification circuit 2, switching means 6 that is disposed at the AC source 1 side from the smoothing capacitor 4, a reactor 3 that is disposed at the power source side from the switching means 6, load amount detection means 10 that detects load amount of the load connected in parallel to the smoothing capacitor 4, and control means 8 that performs opening and closing control of the switching means at least twice in half a cycle of the power source in synchronization with the power source period of the AC source 1 in an opening and closing time according to load amount.” (Patent Literature 2)
Furthermore, as a technique intended “to provide a power unit that can smoothly adjust a wide range of output voltage from a voltage by full-wave rectification to not less than the voltage by voltage doubler rectification while performing power factor improvement with a simple configuration and satisfying restrictions on harmonics”, the technique is proposed such that “a switch SW1 connected between an input terminal of a rectification circuit 2 and a connection point between capacitors 4 and 5 for voltage doubler and the switch SW2 connected between the other input terminal of the rectification circuit 2 and the connection point between capacitors 4 and 5 are provided in a power unit. In an operation mode 1, the switch SW1 is controlled continuously to be on from a zero-cross time of a supply voltage only for an on-period in which the voltage varies according to an output voltage, and the switch SW2 is controlled to be always off. In an operation mode 2, the switch SW1 is controlled continuously to be on from a zero-cross time of a supply voltage only for an on-period, and the switch SW2 is controlled to be always on.” (Patent Literature 3)
Moreover, as a technique intended “to provide an inverter air-conditioner capable of achieving a maximum rotation speed increase of a compressor with a simple configuration, high power factor, harmonics suppression, and expansion of a variable range of an output voltage”, the technique is proposed such that “a capacitor circuit connected between two output terminals of a rectification circuit, first switching means 7 connected between one input terminal of the rectification circuit and a connection point in the capacitor circuit, and second switching means connected between the other input terminal of the rectification circuit and the connection point in the capacitor circuit are provided. By switching the first and the second switching means 7 and 8 suitably, high power factor and harmonics suppression become compatible and maximum ability and efficiency of the air-conditioner can be improved.” (Patent Literature 4)
Moreover, as a technique intended “to make it possible to generate a voltage which is equal to or larger than an input voltage in a converter circuit converting an output voltage of an AC source 1 without using a reactor and a large capacity capacitor”, the technique is proposed such that “in the converter circuit 100 converting the output voltage of the AC source 1, there are provided a rectification circuit 20 for rectifying the output voltage of the AC source 1, a first and a second capacitors 31 and 32 connected in series for smoothing the output of the rectification circuit 20, and a switching circuit 40 for switching the connection between the above both capacitors 31 and 32 and the AC source so that the output voltage of the AC source 1 is alternately repetitively applied to the first and the second capacitors 31 and 32 with a period shorter than that of the AC source.” (Patent Literature 5)
Moreover, as a technique intended “to provide a power unit that satisfies power line harmonics regulations and in which boosting performance and input power factor of the power unit can be compatible at a high level”, the technique is proposed such that “in a power unit comprising; a rectification circuit, a capacitor circuit constituted by a plurality of capacitors connected in series, being connected between two output terminals of the rectification circuit, first switching means connected between either of the input terminal of the rectification circuit and one connection point between capacitors in the capacitor circuit, second switching means connected between the other input terminal of the rectification circuit and one connection point between capacitors in the capacitor circuit, and zero-cross detection means that detects a zero-cross point of the AC source, for each half a cycle of the AC source, after both the first and the second switching means are powered on for a predetermined time t1 after a zero-cross point of the AC source, and after the second switching means is powered off for a predetermined time t2, the first and the second switching means 7 and 8 are powered off.” (Patent Literature 6)
A technique is proposed that controls the input current to be almost sinusoidal and suppresses harmonics to improve power factor by performing high-frequency PWM (Pulse Width Modulation) operation of switching means. (Patent Literature 7)
As a technique whose problem is that “in a configuration where a full-wave rectification circuit constituted by a single-phase AC power unit and diodes, a reactor, a capacitor series circuit, a bi-directional switch, and a load are connected, when making an AC input current to have a high power factor by switching the bi-directional switch, the voltage of the capacitor connected in series becomes imbalanced during a half-cycle period”, the technique is proposed such that “in a configuration such that a reactor is connected with one of the AC input terminals of a full-wave rectification circuit composed of a single-phase AC power unit and diodes, a capacitor series circuit is connected between the DC output of the full-wave rectification circuit, bi-directional switches 10 and 11 are connected between internal connection points of the capacitor series circuit and each AC input of the full-wave rectification circuit, and a load 14 is connected in parallel with the capacitor series circuit, respectively, voltages of the capacitors 12 and 13 connected in series are detected and bi-directional switches 10 and 11 are on-off controlled at high frequency in such a way that the voltages become even” (Patent Literature 8)
A technique is proposed that suppresses a harmonic current by operating two switching elements. (Non-patent Literature 1)